1. Field of the Invention
This invention pertains to fluid spraying generally, and more particularly to a gas separation filter having in combination a restrictor valve and a pressure gauge port, which is most preferably used in combination with a pneumatically powered paint sprayer and may additionally be used with other pneumatic devices.
2. Description of the Related Art
Compressed air has been used for many years in a number of diverse applications. As a source of energy or power, compressed gases offer significant advantage over electricity in safety and convenience in a work environment. For example, in a garage or other shop occupied by work tools, movable carts and vehicles, electrical insulation is readily damaged and metal conductors only offer limited flexibility. So when a vehicle or cart traverses over an electrical line, any persons present and the vehicle or cart are exposed to potentially hazardous electrical energy. Furthermore, with repeated flexing or possible kinking of the electrical cabling, metal conductors may become separated and prone to overheating or arcing, either which might result in fire. In contrast, a pneumatic line or air hose is generally fabricated from a rubber or other similar elastomeric compound which offers nearly limitless resiliency and strength, substantially greater than obtainable with electrical insulation. Even in the event an air hose is damaged, a small stream of air is released, which would only extremely rarely ever present a hazard.
Electrical tools and appliances often also generate sparks or small arcing during power switching or during motor operation, the arcs which act as a further hazard when flammable liquids or vapors are present. In many automotive and paint shops, solvents and fuels are omnipresent, thereby restricting the number and types of electrical tools that are present. In addition, when a pneumatic tool binds, no further activity or hazard is generated. However, when an electrical tool binds, frequently there is an increase in the amount of electrical power being delivered to the tool accompanied by a decrease in internal cooling, which is usually provided as a by-product of tool motion. This adverse combination also leads to over-heating and early failure of electrical tools. An electric motor additionally requires a relatively significant amount of space and mass, whereas a pneumatic motor is frequently smaller, simpler and lighter.
In spraying paint and other liquid or powder media, compressed air offers several additional advantages. Among these are the ability to form a very fine mist or particulate stream with the liquid or powder media, where the particles are well dispersed in the high velocity air stream. Some control is possible in the characteristics of the mist, as a result of gas pressure and particulate feed rate. Changes such as these are made to adjust the characteristics of the resultant film formed by the spraying.
Nevertheless, in spite of the many advantages offered by compressed air, some disadvantages are also inherent in the system. First and foremost is the possibility of contamination of the air stream. Larger particles, such as rust flakes from a corroded air tank, accumulated dust, or hose wear products may cause clogging, jamming or other device malfunction. Liquid condensation presents another formidable obstacle to those wishing to use compressed air, acting as a different form of air stream contamination. When air is compressed, a certain amount of heat is generated in the compression process. During this time, moisture contained therein may be preserved in vapor form. However, once the compressed air cools, such as might occur in a pressure tank or at the air outlet of a pneumatic device, some of the moisture will condense therefrom. This condensation may occur directly in the pressure tank, or may alternatively occur in the air hoses which distribute the compressed air to tools and other appliances. When a high speed pneumatic tool is exposed to this moisture, there is a possibility of either removing some of the necessary lubricant from the pneumatic engine or possible internal corrosion. As a result, many tool air lines include an in-line oiler which introduces additional lubricant to the tool. In the painting industry, the moisture may result in a blistering of the paint, and, if the paint is a primer or similar base coating, the moisture may have direct access to the substrate to accelerate corrosion thereon. Further compounding matters, the in-line oiler used in the tool industry is incompatible with later use of a paint sprayer, due to the presence of the lubricant in the line and the adverse affect it has on paint and other finishes. Clearly, the presence of moisture and other contaminants is highly undesirable.
To prevent the passing of moisture through the air stream to the pneumatically powered tool or apparatus, a number of filters and condensation traps have been devised in the prior art, each of which are incorporated by reference hereinbelow for their content and teachings of the art of gas separation. Representative of these is the air modifier of U.S. Pat. No. 1,255,533 to Heinrich, which illustrates an air inlet, in-line filter and pressure valve all integrated into a single structure. A stop cock is provided at a bottom end opposite the air inlet and outlet which may be used to purge the modifier of accumulated moisture. Unfortunately, the Heinrich device inefficiently uses space and so has little application at the point of use of the device. As a result, condensation that occurs in transit from the tank through the hose to the device will not be removed by the Heinrich device, which must reside adjacent the tank or at some distribution point remote from the pneumatic tool. In addition, the Heinrich device has a fairly complex construction and filter arrangement, each of which add initial expense and which also encumber routine maintenance such as a filter change. Other similar devices which serve to filter an air stream but which are inappropriate for point of use applications are illustrated by Nolden in U.S. Pat. No. 1,091,695; Shaw in U.S. Pat. No. 2,669,320; and Wilkins in U.S. Pat. No. 2,880,753.
Several devices which more directly address point of use are illustrated by Shada in U.S. Pat. No. 2,920,716; Hermann in U.S. Pat. No. 1,822,622; and Overby in U.S. Pat. No. 4,810,272, each which illustrate valves in combination with in-line filters and paint sprayer handles, though none disclose a gauge port. Unfortunately, Shada offers no way to readily remove accumulated liquid, and Hermann and Overby each require a specific tool designed around the filter and valve combination. In U.S. Pat. No. 3,920,189 to Maggiacomo et al, a filter retrofittable to a sprayer handle includes a restrictor valve, though the filter is of the cotton batting construction, which again encumbers replacement thereof. In addition, these prior art filters which incorporate cotton batting or cotton string provide substantial inherent flow restriction, which is a significant disadvantage in the newer High Volume Low Pressure (HVLP) paint guns. In addition to the poor filter material and efficacy, diameter restrictions were generally necessitated by the tendency of the filter material to extrude into openings and orifices under pressure. Furthermore, needle valves of the prior art are inherently small and limited in orifice cross-section. These types of valves are also particularly disadvantageous. While each of these prior art references enabled various respective advancements, none has proven satisfactory as a retrofit, particularly in the demanding art of paint spraying.